My 1996 RZN185 Hilux Surf (JDM 4Runner) is only just scraping past the UK CO emissions regulation (0.20 % at fast idle) and I'd like to replace the catalytic converter. Unfortunately the original part is no longer available, and I will not consider a non-Toyota catalytic converter.

My original is small in size with 4 rows of perforations on the heatshield. From what I see, all US market 3RZ-FE 4Runners, in fact almost all other 4Runners and Landcruiser Prados with the same engine and frame, have a larger catalytic converter with 8 rows of perforations on the heatshield.

I have both options (small and large) available and am not sure which to go for. I would like to get my emissions down but not add further restrictions to the exhaust system.

Any idea if the bigger catalytic converter is likely to add more restriction, or could it in fact flow better?

Thanks

EO

What you're probably seeing is the cats made for California spec and Federal spec. California had harsher standards, so Toyota only put the expensive cat on cars that were sold there.

I've never heard that one made less power than the other, but the cost was certainly different.

I'm going to assume either will meet the emission standard you need to meet. US market cars during that era made less power than European versions because of the emissions standard (E36 M3 example), so even a federal cat should be good enough.